TP-6391 9/0848 Section 5 Component Testing and Adjustment
9. Use a megohmmeter to determine whether the
stator is shorted to ground.
a. Apply 500 volts DC to any stator lead and the
stator frame. Perform the megohmmeter test
following the instructions of the megohmmeter
manufacturer.
b. Repeat the test on the other stator leads until
each coil is tested.
Note: A reading of approximately 500 kOhms
(1/2 megohm) and higher indicates a
good stator.
c. Repair or replace the stator if any reading is
less than approximately 500 kOhms. A reading
of less than 500 kOhms indicates deterioration
of the winding insulation and possible current
flow to ground.
3
4
55
2
1
44
11
6198
66
Figure 5-5 Single-Phase Alternator Stator Leads
Leads Continuity
1 and 2
1 and 11
2 and 11
3 and 4
Yes
3 and 44
4 and 44
55 and 66
1 and 3, 4, 44, 55, or 66
2 and 3, 4, 44, 55, or 66
3 and 1, 2, 11, 55, or 66
4 and 1, 2, 11, 55, or 66
Any stator lead and ground on stator
housing or frame laminations
Figure 5-6 Continuity Test Results on a Good Stator
(Single-Phase)
5.4 Main Field (Rotor)
The two-pole rotor creates the magnetic field needed to
produce alternating current in the stator windings.
Before testing, inspect the rotor for visible damage to
pole shoes, insulation, exposed coil windings, and slip
ring surfaces. Rotate the bearing to check for wear, heat
discoloration, or noise.
5.4.1 Rotor Continuity and Resistance
Tests
Hazardous voltage.
Can cause severe injury or death.
Operate the generator set only when
all guards and electrical enclosures
areinplace.
Moving parts.
WARNING
High voltage test. Hazardous voltage can cause severe
injury or death. Follow the instructions of the test equipment
manufacturer when performing high-voltage tests on the rotor
or stator. An improper test procedure can damage equipment
or lead to generator set failure.
Grounding electrical equipment. Hazardous voltage can
cause severe injury or death. Electrocution is possible
whenever electricity is present. Ensure you comply with all
applicable codes and standards. Electrically ground the
generator set, transfer switch, and related equipment and
electrical circuits. Turn off the main circuit breakers of all
power sources before servicing the equipment. Never contact
electrical leads or appliances when standing in water or on wet
ground because these conditions increase the risk of
electrocution.
Rotor Test Procedure
1. Place the generator set master switch in the OFF
position.
2. Disconnect power to the battery charger, if
equipped.
3. Disconnect the generator set engine starting
battery, negative (--) lead first.
4. Remove the brush cover from the alternator end
bracket.
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